Spot weld recorder



Nov. 29, 1938.

c. E. HEITMAN. JR

SPOT WELD RECORDER Filed Aug. 5, 1935 8 )8 a a qw H 3 l N VEN TOR CH RmsE.HEITMAN,JR.

. BY ATTORNEY.

Patented Nov. 29, 1938 2,138,790

UNITED STATES PATENT OFFICE sro'r WELD RECORDER Charles E. Heitman, Jr.,Philadelphia, Pa., assignor to Edward G. Budd Manufacturing Company,Philadelphia, Pa., a corporation of Penn-' sylvania Application August5, 1935, Serial No. 34,760

15 Claims. (Cl. 177-311) The present invention relates in general to ingmeans to permit the measuring means to electrical resistance welding andmore particuassume normal position between such repeated larly to highspeed spot welding. connections.

In the copending application of Earl J. W. The invention is illustrateddiagrammatically Ragsdale and Charles E. Heitman, Jr., Serial No. in theaccompanying drawing. 5 621,318, filed July 7, 1932, is disclosed inappa- While the invention is here shown as used in ratus for indicatingand recording the welding connection with a timer of the Thyratron type,heat units consumed in a weld contemporaneit is to be understood that aparticular type of ously with the flow of current effecting the weld,timer is not essential, and that the invention particularly a spot weldor other weld of short may be used with any type of timer including 10duration, even though the welding operation is the various kinds ofmechanical timers. shorter than the full response of the recordingReferring to the diagram in detail, the welding apparatus. However, suchapparatus in itself is electrodes l are supplied with current from theinapplicable to systems where the welding cursecondary of the weldingtransformer 2, over rent impulses or undulations for the individualleads 3-4, the primary of the welding transl5 welds occur in such rapidsuccession that the former being connected over leads 5.-6 throughinterval between impulses is insufficient to give switch contacts '|8 toa source of alternating the indicator time to return to normal position,current power supply 9. Timing of the current This is particularly thecase where spot welds flow through the primary winding of the weldingare made in rapid succession as in the forming transformer 2 is effectedthrough the use of a 20 of a series of spot welds by an automaticmachine Thyratron timer ill operative to repeatedly either as relativelywidely spaced welds, or closely close and open the circuit of thesecondary windspaced or overlapping welds as in a seam welder, ing of aseries transformer H whose primary in which latter the welding currentimpulses d g s eenneeted n Series With the e d may be either entirelydiscrete, or may be in transformer supply circuit 56 to vary the im- 25the form of undulations similar in effect to impedance thereof to theextent of cutting on and pulses overlapping in point of time.substantially completely cutting off the current It is therefore thechief object of the present supply to produce the desired weldingcurrent iminvention to provide in such a high speed system, pulses, forexample, impulses of 4 cycles on with a means and method of indicatingand/or reno current or substantially no current intervals 30 cordingcertain characteristics of the welding of 3 c e t e e rod s l are ose oa current impulses such as the welding heat units seam welding machineor the like. The Thyraused in an individual weld, regardless of whethertron timer I0 is also arranged in any known or the interval betweenwelding operations is less other suitable manner to supply impulses ofalterthan the full response period of the measuring nating current ofrelatively low voltage, con- 35 means, and to do this concurrently withthe welden ently derived from the source 9. Over the ing operations sothat the operator will be ap- Quit in synehlenism and contemporaneousprised immediately of the occurrence of a faulty with the weldingcurrent impulses for a P p operation and may remedy the fault beforefurto be ereinafter des r e ve p 40 ther progressing with the work. Ition of the timer will suifice for a clear under- 40 Other objects andadvantages of the invention standing of the invention inasmuch as thetimer will be apparent from a perusal of the following ID with its coupg transformer ll may be respecification and the drawing accompanying thplaced by any known or other suitable form of ame 1 timer capable ofeffecting a periodic closing and I attain the main object of. myinvention by opening of theprimary circuit of the welding providingsuitable means for measuring the detransformer or variation of impedancethereof, sired characteristics, for example, means for inwhile supplyingsynchronous control current imtegrating the total welding heat units ina weldpulses over the leads l2-l3. ing current impulse, with means forrepeatedly Electrical energy proportional to the current efiecting anoperative connection of the measurflowing through the leads 34 is takenoff 50 ing means with the welding circuit each time through a seriestransformer l4 and led through for a period so timed with respect to thewelding conductors I5-l6 to an energy indicating current impulses as toinclude only one impulse, and recording meter N. This indicating deandat intervals of a suflicient length of time vice is of the type shownand described in 5 with respect to the time constants of the measurthecopending application above mentioned and comprises-in general aseries-type motor relay having a spring biased rotor I8 carrying acontact member l9 and suitable recording stylus not shown, the contactmember being arranged to sweep over a pair of signal control contacts 20and 2| in succession. The stator 22 is provided with a series winding 23connected in series with the winding of the rotor l8 and the secondaryof the series transformer |4 through conductors |5| 6. The rotor arm 24through which the rotor carries the contact I9 is biased in the positionindicated by a suitable biasing or retractile spring 25. A recordingtape with which the recording stylus cooperates and means for feedingthe tape preferably as shown and described in the above-mentionedcopending application are not shown here inasmuch as they do not form anessential part of the present invention and may be of any known or othersuitable form operable to provide a continuous record of the differentmeter readings. However, where such a recording tape or the like is usedit is desirable that it be moved once for each actuation of the meteringdevice and at a time when the stylus is not in motion and to this endsuitable electromagnetic tape moving means is provided and arranged tobe operated in timed relation to the operation of the metering device.It therefore suffices simply to indicate such an electromagnetic, tapemoving means diagrammatically as an electromagnet 26 in order to showits circuit connections and the timing of its operation in relation tothe operation of the system.

Due to the series connection of stator and rotor, the mass inertia ofthe moving parts and the properly adjusted tension of the retractilespring 25, the throw of the rotor arm 24 is proportional to the squareof the current multiplied by time, and as this current is proportionalto the welding current, the throw of the arm 24 constitutes acomparative heat units indicator responsive to the current in thewelding circuit and the duration thereof. The stationarycontact 20 isplaced at a point in the path of movable con-. tact l9 representing apredetermined standard of weld perfection while the contact 2| is placedfurther on in the path of contact l9 at a point representing a totalconsumption of energy sufficiently great to cause a burn or overheatingof te metal at te weld. Preferably te contact 2| is placed at a point upto which the position of the movable contact l9 would represent a weldwithin the margin of standard quality.

Inasmuch as the meter I! must integrate the complete current-time valueof an entire welding-current impulse its period of complete responsemust be sufficient to cover the entire period of the welding-currentimpulse, and as these impulses occur in rapid succession with intervalsless than the impulse periods, the meter l1 and associated circuits andapparatus elements will not respond to successive weldingcurrentimpulses in a manner to give accurate readings. To make possible anaccurate response of the meter regardless of relatively high periodicityof the welding-current impulses and relatively short intervals betweenimpulses,

means are provided for repeatedly effecting an operative connection ofthe meter I! with the welding circuit each time for a period so timed inrelation to the welding current impulses as to include only one completeimpulse and at intervals longer than that between such impulses and ofsufficient lengthof time to permit the meter l1 and its associatedcircuits andapparatus elements to assume normal conditions between suchrepeated connections. The means for accomplishing this comprises astep-by-step commutating switch 21 operated in synchronism with thewelding-current impulses by the synchronized impulses of alternatingcurrent supplied by the timer over conductors |2|3. The switch isoperated by a direct-current stepping magnet 28, the spring retractedarmature of which carries a stepping pawl 29 arranged to operativelyengage the driving ratchet 30 of the switch 21. The impulses ofalternating current are fed to the stepping magnet 28 through a suitablerectifier assemblage 3| and effect one operation of the magnet at eachimpulse. In order that the stepping of the switch will occur only duringthe intervals between welding current impulses the pawl and ratchet arearranged to operate on the back stroke as indicated in the diagram.

The ratchet element 30 carries a pair of diametrically arranged radialwiper arms 3|-32 which sweep over a series of fixed contacts so arrangedin a semi-circular bank that as one wiper arm leaves the last contact inthe bank, the opposite arm will engage the first contact in the bank.Electrical connection with the wiper arms is maintained through brush 33permanently connected to binding post terminal 34. Certain selectedcontacts of the bank of fixed contacts or groups of such contacts,suitably spaced in the semi-circular bank such as the groups 35 and 36are connected in common to the terminal 31 which connects over lead 38to terminal 39 from which the connection branches to the recordtapefeeding magnet 26 and to a normally closed contact on the under-weldsignaling relay 40. Contacts 4| and 42spaced slightly beyond the contactgroups 35 and 36 preferably spaced from the latter by at least one deadcontact 'are connected in common through conductor 43 to control relay44 for maintaining the latter energized during a selectedwelding-current impulse which relay controls a shunt across theterminals of the series transformer l4 through a normally closed or backcontact 45 whereby during the dwell of one of the wiper arms on acontact 4| or 42, the output of the transformer will be directed throughthe meter H.

The under-weld signal relay 40 is arranged to lock itself up through arelease relay 46 controlled through normal-weld contact 20 of the meterfor release of the relay 40 upon arrival of the meter contact l9 at thecontact 20, while over-weld signaling relay 41 is arranged to beenergized through over-weld contact 2| and lock itself through a frontcontact 48. A suitable signal such as the audible signal indicated at49, such as an electric bell is connected over conductors 50 and 5| tofront contacts 52 and 53 on under-weld relay 40 and over-weld relay 41,

' respectively, for control in common thereby.

The system as a whole is controlled through a control switch 54 in arelatively low voltage control circuit which through suitable step uprelays 55 and 56 controls the actuating magnet 51 of anelectromagnetically operated power supply switch 58. Whereas in thepresent instance a timer of the Thyratron" type is used, a high voltageexists in the timer circuits due to the high ratio between the secondarywinding of the series transformer II and its primary winding in the'power circuit, and to guard the operator against contact with such highvoltage that portion of the circuit in which it exists is, in practice,housed within the cabinet of the timer l0, and the door of the cabinetarranged to control a safety door switch 59 operable to prevent closureof the control circuit while the cabinet door is open.

In operation, assuming that the safety switch 59 has been closed byclosure of the cabinet door of the timer, the operator desiring to startwelding operations closes the control switch 54 which energizes relay 55by low voltage current from the step-down transformer 68 which latter isenergized from the power lines 6|-62 over conductors 6364 and 65-66.Relay 55 attracting its armature completes the energizing circuit ofrelay 56 supplied from conductors 65-66 which latter relay uponenergization, completes the energizing circuit of the magnet 51 of theelectromagnetic power switch 58 which energizing circuit may be tracedfrom conductor 65, through contact 68, magnet 51, contact 69 toconductor 66. Energization of the magnet 51 closes the power switch 58which connectsthe primary circuit of the welding transformer 2 to thepower lines 6I-62 by way of conductors 6364, switch contacts 1-8 andconductors -6; and completes the actuating circuit of the step-by-stepswitch 21 at contact 18.

The primary winding of the welding transformer 2 being now connected tothe power lines,

the welding transformer through control of the timer operates to supplywelding current impulses through the electrodes I over the weldingcircuit 34. During each welding impulse a control impulse is sent overthe conductors I2- I3 energizing the stepping magnet 28 to actuate thestepping pawl 29 which upon each back stroke steps the wiper arms of theswitch 21 around from one contact to the next. The energizing circuit ofthe magnet 28 may be traced from conductor I2, through rectifier 3|,conductor 1|, magnet 28, conductor 12, rectifier 3|,

conductor 13 and the switch contact 18 back over conductor I3.

While the system is thus operating, with the wiper arm 3| sweeping overthe dead or unconnected contacts such as 14, the meter I1, tape feedingmagnet 26 and the relays 48, 46, 41 and 44, are in the normal positionshown. Upon arrival of the wiper arm 3| at the first of the group ofcontacts 35, the tape feeding magnet 26 is energized to step the recordtape, While at the same time the under-weld signal relay 48 is alsoenergized. The energizing circuit of magnet 26 may be traced from powerline 6| through conductor 63, contact 1, conductor 15, terminal 34,brush 33, wiper arm 3|, contacts 35, conductors 16, 38, terminal 39,magnet 26, terminal 11, switch 18, terminal 19, conductor 88, contact 8,conductor 64, back overpower, line 62. The energizing circuit of relay48 may be traced from thence to power line 62 as before traced. The

relay 48 upon energization opens its initial energizing circuit at backcontact 8| but immediately closes a locking circuit for itself throughits front contact 85 and a back contact of release relay 46 whichlocking circuit may be traced from power line 6| to terminal 34 aspreviously traced and thence over conductor 86, 81, terminal 88,conductor 89 back contact of release relay 46, contact 85 of relay 48,winding of relay 48, thence to conductor 82 to power line 62as-previously traced. Energization of relay 48 also completes thecircuit of the audible signal 49 which may be traced from power line 6|to terminal 88 as previously traced and thence over conductor 98,contact 52 of relay 48, conductors 5|, 58, signal 49, conductor 84,terminal 11 and thence to power line 62 as previously traced.

To insure ample time for the operations just described a suitableplurality of contacts are included in the group 35. After the wiper arm3| leaves the last of the group of contacts 35 the relay 48 remainslocked in its energized position, so that the signal 49 also remainsenergized. However, the signal 49 gives little or no response before thewiper arm 3| engages the contact 4|. Upon engagement of the wiper armwith the contact 4|, the circuit of the meter-control relay 44 isclosed, which circuit may be traced from power line 6| to wiper arm 3|as before traced and thence through contact 4|, conductor 9|, conductor43, winding of relay 44, conductor 84, terminal 11 and thence to powerconductor 62 as previously traced. Relay 44 upon energization opens itsback contact 45 removing the shunt from across the terminals of theseries transformer I4 permitting the full output of such transformer topass to the meter I1 over conductors I 5I6.

The operation of the various parts are so timed in relation to eachother that the wiper arm 3| stepping between welding impulses arrives atthe contact 4| before the beginning of the next welding impulse andremains thereon until the next interval between impulses when it stepsoff the contact permitting relay 44 to again close the shunt, with theresult that the shunt circuit through contact 45 of the relay 44 isopened before the beginning of a Welding impulse and remains open duringthe entire impulse period, closing after the impulse has ceased andbefore the beginning of the succeeding impulse. the entire energy of a,single welding-current impulse is measured by the meter I1.

The meter I1 receiving the output of the series transformer I 4 respondsthereto by a swing of the contact I9 to the left in proportion to theweldingheat units or current-time value of the welding-current impulse.If this value is suflicient to represent the predetermined standard ofweld perfection within a given permissible margin, the swing of thecontact I9 will be sufiicient to reach or pass over the contact 28 butwill not reach the contact 2|. Engagement of contacts I 9 and 28,energizes release relay-46 over a circuit which may be traced from powerline 8|, to terminal 34 as previously traced, thence over conductor 86,contacts I 928, conductor 92 relay 46, 83, 84 to terminal 11 and back topower line 62 as previously traced. The release relay 46 attracting itsarmature opens the back contact thereof, thus opening the lockingcircuit of the under-weld signaling relay 48 which latter releasing it'sarmature opens the circuit of signal 49 at contact 52. As the groups ofcontacts 35 and 36 are connected in multiple and contacts and 42 areconnected in multiple, the above testing operation is repeated each timeone of the wiper arms 3| or 32 sweeps over one of the sets of contacts354I or 36-42, so long as the welding operations are proceeding. Thesetesting operations are repeated at a frequency determined by the angularspacing between similar test control contacts on the switch 21, forexample, contacts 42 and. Preferably the switch is so arranged that theintervals will be amply sufficient to give the meter I1 time to give acomplete response at each test and return to normal before the nexttest, at the sametime repeating the Thus 7 tests at a frequencysufficient to avoid undue repitition of any faulty operations.

As the welding operations continue, should faulty operation occur, inthe nature of under welding, engagement of a wiper arm of the switch 21,say wiper arm 32, with the first contact of one of the sets of testcontacts say the first contact of group 36, the under-weld signal relay40 is energized locking itself up through the back contact of releaserelay 4B and energizing the audible signal all as above described. Thewiper arm now engaging contact 42 effects the energization of metercontrol relay 44 whereupon the entire output of the series transformer14 is directed through the meter [1 which this time because of thereduced output of the series transformer does not swing the contact IS asufficient angular distance to reach the contact 20. release relay 46 isnot energized to release the locking circuit of signal relay 40, withthe result that the audible signal 49 continuing energized apprises theoperator of the faulty operation of the welding apparatus. At the end ofthe welding-current impulse just measured, and during the intervalbetween it and the next impulse, the wiper arm 32 moves out ofengagement with the contact 42 which opens the circuit of the relay 44again shunting off the series transformer l4 from the meter [1.I-Iowever, the energizing circuit of signal 49 remains closed until theoperator, having stopped the welding operation,

, opens the switch 18 which as will be remembered is included in andtherefore controls the locking circuit of relay 4D, whereupon relay 40is deenergized as is also the signal 48. After suitable adjustment orrepair necessary to correct the fault causing such warning signal theswitch 18 is again closed and welding operations continued.

Should the faulty operation be that of a burning or overheating, themeter l1 receiving the corresponding increased output from thetransformer l4 will respond by a swing of the contact l9 to or beyondthe contact 2|. Contact l9 passing over contact 20 effects an actuationof release relay 46 releasing the alarm circiut but upon reachingcontact 2| immediately thereafter, completes the energizing circuit ofthe over-weld signal relay 41. This circuit may be traced from powerline 6| to contact l8 as previously traced and thence through contact21, conductor 93, relay 41, conductors 83, 84 to terminal 11 and thenceto power line 62 as previously traced. Relay 41 attracting its armaturecloses the circuit of signal 49 at contact 51 and closes a lockingcircuit for itself through contact 48. The circuit of signal 49 may betraced from power line 6| to terminal 88 as previously traced and thenceover 94, 5|, 50, 49, 84 to terminal 11 and to power line 62 as beforetraced. The locking circuit of relay 41 may be traced from power line 6|to terminal 88 as before and thence over 84, 48, 41, 83, 84 to terminal11 and to power line 82 as before. As the relay 41 now controlling thesignal circuit is locked up, the signal 49 continues to sound after themeter 11 has assumed normal position. The operator noting the continuedsounding of the signal, stops the welding operation and releases thesignal circuit by opening switch 18 which opens that portion of thecircuit of relay 41 traced from relay 41 through 83, 84, 11 and 18.

It will be understood from the above, that any means equivalent infunction may be substituted for the relay 44 and step-by-step switch 21,and that such means may be arranged to eflect the Thus the recurringtests at any frequency of recurrence providing the intervals aresufficient to permit full restoration of the meter and its associatedcircuits and apparatus to normal and quiescent condition between testingperiods. For example, an extra bank of contacts and cooperating set ofwiper arms on the step-by-step switch 21 may take the place of the relay44, and obviously where a mechanical timer is used, a mechanicalswitching element or elements properly synchronized with respect to thewelding-current impulses may replace the step-by-step switch and relay44. Also, a visual or other form of signal may be used instead of ortogether with the audible signal, and different signals may be used toindicate the different conditions respectively. Obviously, the relays 40and 41 may be arranged to control different signals.

While a preferred, specific embodiment of the invention is herein shownand described in detail for the purpose of disclosure, it is to beunderstood that the invention is not limited to such specific embodimentbut contemplates all such modifications and variants thereof as fallfairly within the scope of the appended claims.

What I claim is:

1. In a high speed spot welding system operable to produce spot welds inrapid succession, a welding circuit, a welding heat units indicator andmeans driven in timed relation with the succession of spot weldingoperations for intermittently, operatively connecting the indicator tothe welding circuit, each time during and contemporaneously with onecomplete individual welding period excluding one or more preceding andsucceeding welding periods.

2. In a welding system operable to produce spot welds in rapidsuccession, a welding circuit, means for producing successive impulsesof Welding current in said circuit, a welding heat units indicator, andmeans driven in timed relation with the succession of spot weldingoperations for intermittently, operatively connecting the indicator tothe welding circuit for' periods including and contemporaneous with onecomplete welding current impulse and excluding one or more preceding andsucceeding impulses.

3. In a welding system operable to produce spot welds in rapidsuccession, a welding circuit, means for producing successive impulsesof welding current in said circuit, a welding heat units indicator, andmeans driven in timed relation with the succession of spot weldingoperations for intermittently, operatively connecting the indicator,during a succession of impulses, to the welding circuit for periods eachincluding and contemporaneous with one welding impulse only.

4. In a welding system operable to produce spotwelds in rapidsuccession, a welding circuit,

means for producing successive impulses of welding current in saidcircuit, a welding heat units indicator, and means operated in timedrelation with the succession of current impulses for operativelyconnecting said indicator, during a succession of impulses, with thewelding circuit during and contemporaneously with one complete weldingcurrent impulse only.

5. In a welding system operable to produce spot welds in rapidsuccession, a welding circuit, means for producing successive impulsesof welding current in said circuit, measuring means having a time lag inexcess of the interval between impulses, and means for operativelyconnecting said measuring means, during a succession of impulses, withsaid circuit during and contemporaneously with a period including onewelding impulse only.

6. In a welding system operable to produce spot welds in rapidsuccession, a welding circuit, means for producing successive impulsesof welding current in said circuit, measuring means'for measurpulses andhaving a cycle period longer than the interval between said successiveimpulses, and

ing the current-time product of said welding impulses and having a cycleperiod longer than the interval between said successive impulses, andcircuit control means operating in synchronism with said impulses foroperatively connecting said measuring means, during a succession ofimpulses, with said circuit during and contemporaneously with a periodincluding one welding impulse only for measuring that impulse.

7. In a welding system operable to produce spot welds in rapidsuccession, a welding circuit, means for producing successive impulsesof welding current in said circuit, measuring means for measuring thecurrent-time product of said welding imcircuit control means operatingin synchronism with said impulses for operatively associating saidmeasuring means, during a succession of impulses, with said circuitduring and contemporaneously with a period including one welding impulseonly for measuring that impulse.

8. In awelding system operable to produce spot welds in rapidsuccession, a welding circuit, means for producing successive impulsesof welding current in said circuit, measuring means normally operativelydisconnected from said circuit, means for operatively connecting saidmeasuring means with the welding circuit during a period including andcontemporaneous withone welding impulse only, and signaling means, saidconnecting means being arranged to effect energization of said sig--naling means in advance of the connection of the measuring means andmeans operated by the measuring means to deenergize the signaling meansupon-attainment of a given measured value.

9. In a welding system operable to produce spot welds in rapidsuccession, a welding circuit, means for producing successive impulsesof welding current in said circuit, measuring means normally operativelydisconnected from said circuit, means for operatively connecting saidmeasuring means with the welding circuit during a period including andcontemporaneous with one welding impulse only, signaling means, first'and second locking relays each arranged upon energization to effectenergization of said signaling means, and a control relay arranged uponenergi'zation to open the locking circuit of said first locking relay,said connecting means being arranged to close the circuit of said firstlocking relay in advance of the connection 0! said measuring means, andmeans operated by the measuring means to effect a deenergization of saidcontrol relay upon the attainment of a given measured value and toeffect energization of said second locking. relay upon the attainment ofa higher measured value.

10. In a welding system operable to produce spot welds in rapidsuccession, a welding circuit, means for producing successive impulsesof welding current in said circuit, measuring means for measuring thecurrent-time product of said welding impulses normally operativelydisconnected from said circuit, means for operatively connecting saidmeasuring means with the welding circuit during a period including andcontemporaneous with one welding impulse only, and signaling means, saidconnecting means being arranged to effect energization of said signalingmeans in advance of the connection of the measuring means and meansoperated by the measuring means to effect continuation of theenergization of said signaling means in accordance with the measuredvalue.

11.- In a welding system utilizing a welding cir- V cuit to whichwelding current is supplied in rapidly recurring impulses for producingsuccessive welds, the combination of a welding-heat units indicatorlimited in the time required for a complete operation to a periodgreater than the lapse of time between said current impulses, and meansfor operatively connecting said indicator to the welding circuit duringand contemporaneously with one complete individual welding currentimpulse, excluding one or more preceding and succeeding welding currentimpulses.

12. In a welding system utilizing a welding circuit to which weldingcurrent is supplied in rapidly recurring impulses for producingsuccessive welds, the combination of an integrating welding-heat unitsindicator limited in the time required for a complete operation to aperiod greater than the lapse of time between said current impulses,and.

means responsive to the welding current impulses for operativelyconnecting the said indicator to the welding circuit during andcontemporaneously with one .completeindividual welding impulse,excluding one or more preceding and succeeding impulses.

13. In a welding system utilizinga welding circuit to which weldingcurrent is supplied in rapidly recurring impulses for producingsuccessive welds, the combination of a welding-heat units indicatorrequiring for its full response a period greater than a lapse of timebetween said current impulse and a timing switch operated in response tosaid w'elding current impulses for operatively connecting the saidindicator to the welding circuit during and contemporaneously with onecomplete individual welding impulse,

excluding one or more preceding and succeeding 15. In a welding system,a welding, circuit,

means for producing successive impulses of welding current in saidcircuit, indicating means, switching means for operatively connectingsaid indicating means to the welding circuit, means for operating saidswitching means in response to said impulses, and means for renderingsaid operation eflective to connect the indicating means to the circuitduring and contemporaneously with one complete cycle separated by one ormore preceding cycles and one or more succeeding cycles.

' CHARLES E. HEITMAN, JR.

